The invention relates to a composite plastic panel. More particularly, the invention relates to a composite plastic panel having a protective surface film which is more securely bonded to the base layer as compared to known panels, and to a method for producing such a panel.
It is known to produce plastic panels, in particular panels formed from resins comprising reinforcements such as fiberglass, which have surface films bonded thereto. In the conventional process for manufacturing plastic panels, a first layer, such as a release sheet, generally forming a continuous web, is coated with a thermoset or thermoplastic resin, typically a polyester resin. A reinforcing material may be incorporated into the resin in the form of powders, single or multiple fibers, woven or matted strands or fabric materials.
The composite reinforced resin is covered with a second layer, which may be a film, forming an envelope with the first layer. The envelope containing the liquid resin composition is then formed into the desired shape using techniques commonly known to the industry. The resin/composite matrix is subsequently cured within this film envelope. After the resin has substantially cured, one or both of the layers are removed from the finished reinforced composite plastic panel and recycled or discarded.
Problems can arise when such plastic panels are exposed to moisture, heat, ultraviolet light and abrasion. For example, glass fibers in fiberglass panels may bloom due to the action of moisture, ultraviolet light and heat, resulting in up to a 50% reduction in panel tensile strength. The fiberglass sheet itself may absorb moisture through the surface film or through the edges of the panel. Poor abrasion resistance of some resins results in scratches and other surface defects during manufacturing and installation. These can accelerate panel failure by exposing the reinforcing material to moisture, which may cause it to become separated from the resin binder. Ultraviolet light exposure causes depolymerization and embrittlement of the resin, and also film yellowing, which creates serious light transmission problems in applications on clear panels. While some materials withstand these effects better than others, the majority eventually lose physical properties and appearance characteristics to such an extent that they are no longer useful for their intended applications.
Current practices for bonding a film to a plastic panel have proved inadequate. In particular, the chemical or mechanical bonds of conventional bondable films frequently break down over time, causing the film to discolor, flake off or peel away from the resin surface. Differences in the coefficients of expansion of the plastic sheet and the film also lead to delamination. Separation between the reinforcing film and the core materials results in loss of tensile strength, flexural modulus, impact strength and light transmission properties.